The invention is based on a separable clutch for a motor vehicle, which separable clutch has a clutch adjuster including movably mounted clutch operator for engaging and disengaging the clutch.
A clutch of the above type is known from the Automotive Handbook from Robert Bosch GmbH, 24th edition, page 654. In the single-disk dry clutch shown there, the pressure force is generated by a plurality of coil springs, which are arranged between a clutch cover and a pressure plate. In the engaged state, the clutch springs press the clutch pressure plate against the clutch disk. The hub of the clutch disk is movable on a clutch shaft and transmits the engine torque to the clutch shaft by way of a splined shaft profile.
The clutch adjuster of the clutch is mechanically actuated by virtue of a clutch cable, which is actuated by a clutch pedal engaging on a release fork. The release fork acts at the other side on the rotationally fixedly mounted clutch operator which, in this way, is moved axially and lifts the clutch pressure plate away from the clutch disk counter to the force of the pressure springs in order to release the force-fitting action. However, the clutch disk wears over time, which results in an increasing clutch actuation travel, such that wear adjustment must take place in order to maintain the grabbing point for a defined pedal travel. This is realized in the known clutch in that an adjusting sleeve on the clutch cable is adjusted. Temperature changes in the clutch, for example as a result of intensified use under high load, are compensated in the prior art by clutch play.
In contrast, the object on which the present invention is based is that of further developing a clutch of the above-mentioned type such that the clutch automatically adjusts the respective wear state, including to the respective temperature, and can at the same time be produced more cost-effectively.
The invention is based on the idea that the clutch adjuster is pressure-medium-actuated and includes the following:
a) an actuating piston which acts on the clutch operator for engaging and disengaging the clutch;
b) a pressure chamber which can be acted on with pressure medium and relieved of said action and which is delimited at one side by at least a part of the actuating piston and at the other side by at least a part of a clamping piston;
c) wherein at least the actuating piston, the pressure chamber and the clamping piston are resiliently supported against the clutch operator in a defined position by spring force, which spring force is lower than a limit force required for actuating the clutch operator, and further wherein
d) on account of a pressure change in the pressure chamber caused by a clutch actuation, the clamping piston actuates a clamping device in such a way that the clamping piston is fixed before the actuating piston actuates the clutch operator.
In simple terms, this means that the pressure force of the spring supports the axially movably mounted unit, composed at least of the actuating piston, the pressure chamber and the clamping piston, against the clutch operator in such a way that the clutch operator can duly assume a defined position, but the pressure force is not sufficient to actuate the clutch operator for engaging or disengaging the clutch. The present position of the clutch operator relative to the fixed parts of the clutch is dependent, inter alia, on the present wear state of the clutch and/or on the present temperature of the clutch disk, because wear reduces the thickness of the clutch disk, while high operating temperatures require a greater thickness of the clutch disk. In other words, the relatively low pressure force of the spring ensures that the unit is always supported in a defined fashion against the clutch operator which varies its position as a function of the wear state and the temperature of the clutch.
It is also noted that two functions can be performed simultaneously by a single pressure change, in particular a pressure increase in the pressure chamber. On the one hand, the clamping piston is firstly fixedly clamped in its present axial position, which was hitherto supported only by the relatively low pressure force of the spring, and the pressure chamber which is coupled thereto and the actuating piston which is coupled thereto are thereby also placed into a starting position for the subsequent clutch actuation. The latter is brought about by the same pressure increase in the pressure chamber by virtue of the pressure increase causing a movement of the actuating piston which can be supported against the clamping piston via the pressure medium cushion in the pressure chamber. The movement of the actuating piston brings about an actuation of the clutch operator, which thereupon engages or disengages the clutch.
In contrast, if it were sought merely to adapt the position of the actuating piston to the present wear state, the volume of the pressure chamber would increase with increasing wear, as a result of which the solenoid valves which introduce the pressure medium would have to be designed for the pressure medium volume required for the greatest possible level of wear, and would accordingly be of large dimensions and expensive. Furthermore, such an approach would be associated with disadvantages with regard to the controllability of the pressure medium volume, since the volume would change over time.
However, since, according to the invention, the position of the unit composed of the actuating piston, pressure chamber and clamping piston is adapted to the respective wear and temperature state of the clutch, the volume of the pressure chamber remains substantially constant over the entire wear travel or the entire operating temperature range, which has a positive effect on the pressure medium volume used for actuating the clutch. Not least, the pressure chamber can be of small dimensions, which entails small flow cross sections in the upstream solenoid valves, which can as a result be of very small and cost-effective design.
At least the actuating piston, the pressure chamber and the clamping piston are particularly preferably arranged so as to be movable coaxially with respect to a drive input or drive output shaft, which is assigned to an engine or to a transmission. This saves installation space.
The clamping piston can be supported by the clamping device on a tube piece which is connected to a clutch bell and which coaxially surrounds the drive input or drive output shaft, with it being possible for a force-fitting action, which is based on the principle of a wedge effect, to be produced between the clamping piston and the tube piece by the clamping device. Here, the clamping device may be preloaded by at least one spring in a direction which releases the clamping action.
The spring may be supported at one side on the clutch bell. Furthermore, the pressure chamber may be formed between the actuating piston and the clamping piston, which likewise entails a very compact construction.
According to one particularly preferred embodiment, the actuating piston and the clamping piston are mounted within a cylinder which is axially movable on the tube piece and against which the spring is supported at the other side. The pressure chamber is then delimited radially by a cylinder casing wall of the cylinder, and a pressure medium connection for a supply of pressure medium to the pressure chamber can be formed in the cylinder casing wall.
According to one alternative, the spring may be supported at the other side directly on the clamping piston. The clamping piston is then preloaded by the spring in a direction which reduces the size of the pressure chamber.
More precise details can be gathered from the following description of exemplary embodiments.